Gastric adenocarcinoma is the second leading cause of cancer-related death in the world, and Helicobacter pylori is the strongest identified risk factor for this malignancy, yet only a fraction of colonized persons ever develop neoplasia. One H. pylori determinant associated with gastric cancer is the cag pathogenicity island, and several cag genes encode components of a type IV secretion system which exports bacterial proteins such as CagA into host epithelial cells. Our group has now demonstrated that H. pylori cag+ strains selectively activate ?-catenin and the EGF receptor (EGFR), host effectors that influence carcinogenesis, in gastric epithelial cells. We have also demonstrated that an environmental factor associated with gastric cancer, salt, augments the ability of H. pylori cag+ strains to induce aberrant epithelial responses. Therefore, the overarching objective of this Application is delineation of the molecular signaling events initiated by H. pylori:epithelial cell contact that regulate phenotypes related to gastric carcinogenesis. This PPG will integrate studies of host-pathogen interactions initiated by biomedical researchers who have made a strong and clear commitment to research within the fields of gastroenterology, cancer biology, carcinogenesis, and microbiology, and will generate results that would not be attainable through independent investigation. The component Projects are driven by discrete hypotheses, yet are cohesive in that each focuses on H. pylori:epithelial interactions that induce cellular responses with carcinogenic potential. The individual projects include: Project 1. Mechanisms that regulate Helicobacter pylori-induced ?-catenin activation (PI-Richard Peek). Project 2. EGFR activation in H. pylori-induced gastric cancer (PI-Brent Polk). Project 3. Helicobacter pylori cag pathogenicity island and gastric carcinogenesis (PI-Timothy Cover). The efforts of each Project will be further unified by dynamic interactions with Specific Core facilities, which include the Gastric Histopathology Core (Core A), the Proteomics Core (Core B), and an Administrative Core (Core C). By maintaining a grounded focus on fundamental interactions that occur at the H. pylori:epithelial interface, results from this proposal will not only improve our understanding of gastric cancer, but will also facilitate identification of potential therapeutic targets for prevention and more effective treatment of this disease.